WASHINGTON — Several lawmakers expressed alarm Tuesday with President Donald Trump’s plans to halt military exercises with U.S. ally South Korea following his historic summit with North Korea’s Kim Jong Un, with some of them arguing any deal has to be ratified by Congress.

Among them, Sen. David Perdue, R-Ga., a member of the Senate Armed Services Committee, said he was caught off guard since Trump had said military cooperation would not necessarily be part of a first meeting with Kim.

“I’m very troubled today. This concession today, I was surprised frankly,” Perdue said during a breakfast meeting with reporters. “But I don’t think it’s as big a deal as it might appear this morning, just because we have so many other things in the region. However, the coordination with the South Korean military is absolutely critical.”

On Tuesday, Trump stunned some watchers of the summit in Singapore when he said the United States would suspend joint exercises with South Korea, making a major concession to the North while seemingly receiving nothing in return. The move would reverse decades of U.S. military posture in the region, with joint exercises at the heart of readiness efforts against the rogue regime’s artillery and more than one million soldiers.

The drills infuriate Pyongyang, which considers them a rehearsal for an invasion of the North.

“It’s clear that Kim Jong Un walked away from Singapore with exactly what he wanted – the pomp, circumstance and prestige of a meeting with the president of the United States – while making no specific commitments in return,” said Sen. Mark Warner, D-Va. “Whether this will result in a verifiable agreement to dismantle North Korea’s nuclear weapons program, America and the world will wait to find out.”

Senate Minority Leader Chuck Schumer, D-N.Y., said he was concerned that none of North Korea’s human rights violations were addressed. Instead, he said Trump offered to end military exercises “in exchange for the mere hope that North Korea will freeze its illegal nuclear testing regime.”

“What the United States has gained is vague and unverifiable at best. What North Korea has gained, however, is tangible and lasting,” Schumer said from the Senate floor. “By granting a meeting with Chairman Kim, President Trump has granted a brutal and repressive dictatorship the international legitimacy it has long craved. The symbols that were broadcast all over the world last night have lasting consequences.”

The United States has about 28,500 servicemembers in South Korea as part of the longstanding alliance between the two countries that fought together in the Korean War, which lasted from 1950 to 1953. Trump said he has no plans to decrease the number of U.S. troops in the South as part of security assurances for the North, but he left open the possibility that he will do so in the future.

Rep. Mac Thornberry, R-Texas, chairman of the House Armed Services Committee, warned the United States should proceed cautiously.

“It is perfectly reasonable to hope that we are seeing the beginning of a process that will lead to a complete, permanent, verifiable end to North Korea’s nuclear capabilities. It is also perfectly reasonable be skeptical of North Korea’s intentions, given its history of broken agreements,” Thornberry said in a prepared statement. “The key going forward will be North Korea’s actions, not their promises, in taking concrete, transparent steps toward that goal. In the meantime, it is essential to maintain economic sanctions and diplomatic pressure, and above all to continue strengthening our military capability to defend ourselves and our allies.”

Perdue and others said any negotiations should focus on economic efforts, not military operations. The troops and joint exercises were not mentioned in the final summit document, which focused on security guarantees and a general commitment to denuclearization.

“This was an historic first step in an important negotiation,” said Senate Majority Leader Mitch McConnell, R-Ky. However, “if North Korea does not prove willing to follow through, we and our allies must be prepared to restore the policy of maximum pressure.”

House Speaker Rep. Paul Ryan agreed a successful deal with the North will take time.

"As negotiations now advance, there is only one acceptable final outcome: complete, verifiable, irreversible denuclearization,” said Ryan, R-Wisc. “We must always be clear that we are dealing with a brutal regime with a long history of deceit. Only time will tell if North Korea is serious this time, and in the meantime we must continue to apply maximum economic pressure. The road ahead is a long one, but today there is hope that the president has put us on a path to lasting peace in the Korean Peninsula."

Washington and Seoul conduct two major sets of military exercises each year — Foal Eagle and Key Resolve in the spring and Ulchi Freedom Guardian in the fall. They also hold smaller training exercises throughout the year.

Trump hasn’t offered details about halting the exercises, which were already disrupted this year when springtime drills were delayed for the Winter Olympics, which took place in South Korea. The United States also canceled the exercises several times in the 1990s as part of negotiations with the North that eventually collapsed.

“The idea that the president said this might be on the table doesn’t mean that it’s a signed part of any agreement,” Perdue said. “I wouldn’t be surprised if it isn’t part of the final deal.”

A U.S. Forces Korea spokeswoman said the command had received no updated guidance on the issue, including about the upcoming Ulchi Freedom Guardian exercise that is due to begin in August.

“In coordination with our [South Korean] partners, we will continue with our current military posture until we receive updated guidance from the Department of Defense … and/or Indo-Pacific Command,” Col. Jennifer Lovett told Stars and Stripes in an email.

The Pentagon has yet to announce whether any military exercises will be halted or scaled back.

However, Pentagon spokeswoman Dana White said Tuesday in a prepared statement that "the Department of Defense welcomes the positive news coming out of the summit and fully supports the ongoing, diplomatically led efforts with the Democratic People's Republic of Korea. Our alliances remain ironclad, and ensure peace and stability in the region. The presidential summit outcome is the first step along the path to the goal: complete, verifiable and irreversible denuclearization of the Korean Peninsula and a free and open Indo-Pacific."